I. Technical Field
The present invention relates to a method of manufacturing an impeller that is used in a centrifugal rotating machine such as a centrifugal compressor.
Priority is claimed on Japanese Patent Application No. 2008-259701, filed Oct. 6, 2008, the content of which is incorporated herein by reference.
II. Description of the Related Art
Generally, an impeller that is used in a centrifugal rotating machine has a hub that is attached to a rotating axis, a shroud that is arranged at an interval outward of the hub, and a plurality of blades that couple the hub and the shroud, with a portion that is enclosed by the side surfaces of these blades, the flow surface of the hub, and the flow surface of the shroud serving as a flow passage for compressing air.
The impeller that is used in this kind of centrifugal rotating machine is generally manufactured by fixing, by fillet welding or groove welding, the blades and the shroud to a disk-shaped main body, since the flow passage has a complex shape that curves in the axial direction and radial direction. However, welding defects easily occur in the fixing by the aforementioned welding, and deformation easily occurs due to locally high temperatures.
For this reason, there has been proposed a method for manufacturing that uses electric discharge machining as a substitute means in a method for manufacturing an impeller by welding (For example, see Japanese Unexamined Patent Application, First Publication No. H08-300228 or Japanese Unexamined Patent Application, First Publication No. 2002-235694).
The electric discharge machining method that is disclosed in Japanese Unexamined Patent Application, First Publication No. H08-300228 relates to the manufacture of a steam turbine static blade, and includes the steps of forming a static blade by electric discharge machining from the lower surface side of a partitioning plate disk positioned with the fluid outlet side of the static blade as an upper surface, finishing an edge and a step on the static blade outlet side that are formed by electric discharge machining from the upper surface side of the partitioning plate disk, and then removing the affected layer of the machined surface that is subjected to electric discharge machining by an acid bath. Thereby, a steam passage is formed between the static blades.
The electric discharge machining method that is disclosed in Japanese Unexamined Patent Application, First Publication No. 2002-235694 relates to a rotor for a centrifugal compressor, and has an electrode that has nearly the same shape as a cavity, and forms circular cavities that become flow passages in a disc by electrical erosion with the electrode.